Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulosic materials, such as corn or sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulosic materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulosic material, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol, which is suitable for fuels or human consumption. In addition, fermentation of starchy or cellulosic materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
As an alternative to fermentation, ethanol may be produced by hydrogenating acetic acid and esters thereof. Ethanol production via the reduction of acetic acid generally uses a hydrogenation catalyst. The reduction of various carboxylic acids over metal oxides has been proposed by EP0175558 and U.S. Pat. No. 4,398,039. U.S. Pat. No. 7,608,744 describes a process for the selective production of ethanol by vapor phase reaction of acetic acid at a temperature of about 250° C. over a hydrogenating catalyst composition either cobalt and palladium supported on graphite or cobalt and platinum supported on silica. U.S. Pat. No. 7,863,489 describes a process for the selective production of ethanol by vapor phase reaction of acetic acid over a hydrogenating catalyst composition to form ethanol is disclosed and claimed. In an embodiment of this invention, reaction of acetic acid and hydrogen over a platinum and tin supported on silica, graphite, calcium silicate or silica-alumina in a vapor phase at a temperature of about 250° C. U.S. Pat. No. 6,495,730 describes a process for hydrogenating carboxylic acid using a catalyst comprising activated carbon to support active metal species comprising ruthenium and tin. U.S. Pat. No. 6,204,417 describes another process for preparing aliphatic alcohols by hydrogenating aliphatic carboxylic acids or anhydrides or esters thereof or lactones in the presence of a catalyst comprising platinum and rhenium. U.S. Pat. No. 5,149,680 describes catalytic hydrogenation of carboxylic acids and their anhydrides to alcohols and/or esters in the presence of a catalyst containing a Group VIII metal, such as palladium, a metal capable of alloying with the Group VIII metal, and at least one of the metals rhenium, tungsten or molybdenum. U.S. Pat. No. 4,777,303 describes the productions of alcohols by the hydrogenation of carboxylic acids in the presence of a catalyst that comprises a first component which is either molybdenum or tungsten and a second component which is a noble metal of Group VIII on a high surface area graphitized carbon. U.S. Pat. No. 4,804,791 describes another production process of alcohols by the hydrogenation of carboxylic acids in the presence of a catalyst comprising a noble metal of Group VIII and rhenium. U.S. Pat. No. 4,517,391 describes preparing ethanol by hydrogenating acetic acid under superatmospheric pressure and at elevated temperatures by a process wherein a predominantly cobalt-containing catalyst is used and acetic acid and hydrogen are passed through the reactor, at from 210 to 330° C., and under 10 to 350 bar, under conditions such that a liquid phase is not formed during the process.
Previous hydrogenation catalysts suffered from several drawbacks that did not favor industrial production of ethanol. These drawbacks included low catalyst lifetime, productivity, and co-production of byproducts. One solution for improving productivity and reducing co-production of byproducts, and in particular ethyl acetate, was to enhance the support with a basic modifier. This also increased selectivity to ethanol. Hydrogenation catalysts having supports with basic modifiers have previously been disclosed. U.S. Pat. No. 8,309,772 discloses a process for selective formation of ethanol from acetic acid and includes contacting a feed stream containing acetic acid and hydrogen at an elevated temperature with catalyst comprising platinum and tin on a high surface area silica promoted with calcium metasilicate. U.S. Pat. No. 8,471,075 also discloses a process for selective formation of ethanol from acetic acid by hydrogenating acetic acid in the presence of first metal, a silicaceous support, and at least one support modifier. The support modifier, e.g., metasilicate support modifier, may be selected from the group consisting of (i) alkaline earth metal oxides, (ii) alkali metal oxides, (iii) alkaline earth metal metasilicates, (iv) alkali metal metasilicates, (v) Group IIB metal oxides, (vi) Group JIB metal metasilicates, (vii) Group IIIB metal oxides, (viii) Group IIIB metal metasilicates, and mixtures thereof.
One disadvantage is supports having basic modifiers tend to show a low conversion of acetic acid. Low conversion generally requires a larger acetic acid recycle. Higher amounts of precious metals may be needed to compensate for low conversions. In addition, the hydrogenation catalysts with supports having basic modifiers are not suitable for converting ethyl acetate. Thus, ethyl acetate needs to be removed from the recycle stream to avoid the buildup stream of ethyl acetate in the reactor.
Thus, further improvements to hydrogenation catalysts having supports with basic modifiers to increase conversion of acetic acid are needed to improve production of ethanol from acetic acid.